INSTRUCTION SET OVERVIEW
5-2
5.1.2
Instruction Encoding Formats
All instructions are encoded in one 32-bit machine language instruction — also known as an
opword — which must be word aligned in memory. An opword’s most significant eight bits
contain the opcode field. The opcode field determines the instruction to be performed and how the
remainder of the machine language instruction is interpreted. Instructions are encoded in opwords
in one of four formats (see
Figure 5-1
). For more information on instruction formats, see
APPENDIX C, MACHINE-LEVEL INSTRUCTION FORMATS
.
Table 5-1. Instruction Encoding Formats
Instruction Type
Format
Description
register
REG
Most instructions are encoded in this format. Used primarily
for instructions which perform register-to-register operations.
compare and branch
COBR
An encoding optimization which combines compare and
branch operations into one opword. Other compare and
branch operations are also provided as REG and CTRL
format instructions.
control
CTRL
Used for branches and calls that do not depend on registers
for address calculation.
memory
MEM
Used for referencing an operand which is a memory address.
Load and store instructions — and some branch and call
instructions — use this format. MEM format has two
encodings: MEMA or MEMB. Usage depends upon the
addressing mode selected. Some MEMB-formatted
addressing modes use the word in memory immediately
following the instruction opword as a 32-bit constant. MEMA
format uses one word and MEMB uses one or two words.
Содержание i960 Jx
Страница 1: ...Release Date December 1997 Order Number 272483 002 i960 Jx Microprocessor Developer s Manual ...
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Страница 25: ...1 INTRODUCTION ...
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Страница 35: ...2 DATA TYPES AND MEMORY ADDRESSING MODES ...
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Страница 47: ...3 PROGRAMMING ENVIRONMENT ...
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Страница 73: ...4 CACHE AND ON CHIP DATA RAM ...
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Страница 195: ...INSTRUCTION SET REFERENCE 6 83 6 Opcode mov 5CCH REG movl 5DCH REG movt 5ECH REG movq 5FCH REG See Also LOAD STORE lda ...
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Страница 257: ...8 FAULTS ...
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Страница 493: ...A CONSIDERATIONS FOR WRITING PORTABLE CODE ...
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Страница 503: ...B OPCODES AND EXECUTION TIMES ...
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Страница 515: ...C MACHINE LEVEL INSTRUCTION FORMATS ...
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Страница 523: ...D REGISTER AND DATA STRUCTURES ...
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